This invention relates to improvements in infinitely variable power transmissions and methods for the operation of same. More particularly, it concerns an infinitely variable transmission unit and method for selection of alternate operational modes by which power transmitting efficiencies are improved for any given range of speed ratios within the design limits of the unit.
Mechanical power transmissions which transmit torque from an input to an output at infinitely variable speed ratios are well known in the art and generally referred to as "I.V. transmissions." Because the power generating efficiency of most engines or prime movers is highest in only a limited range of operating speeds, I.V. transmissions have and continue to generate much interest as a potentially ideal solution to the transmission of power from a power source to a power-consuming load which must be driven at speeds varying from the operating speeds of the power source.
Mechanical I.V. transmissions are generally embodied in a structural organization capable of transmitting torque by friction between two or more traction surfaces on relatively rotatable bodies supported in such a manner as to enable the traction surfaces to be retained against one another under a normal force adequate to prevent slippage between the surfaces. The infinitely variable speed ratio is achieved by designing the torque arm or radius of one of the bodies to be continuously variable relative to the radius of the other body. The geometric configuration of two such bodies capable of attaining this result is exemplified by a wheel shiftable axially on a disc or a ring shiftable along the axis of a cone.
In a commonly assigned copending U.S. Pat. application, Ser. No. 706,291, filed July 19, 1976, now U.S. Pat. No. 4,152,946, in the name of the present inventor, several embodiments of infinitely variable transmissions are disclosed in which three frame supported working bodies operate to transmit a mechanical power input to a rotatable output at infinitely variable output/input speed ratios within the design range of the transmission. For purposes of definition in this background discussion as well as in the ensuing detailed description of the present invention and in the appended claims, the three working bodies may be termed respectively, an "alpha body" which is supported by the transmission frame to be concentric with a first axis, a "beta body" which is concentric with a second axis inclined with respect to and intersecting the first axis at a point of axes intersection, and an "omega body" carried by or forming part of the frame to be concentric also with the first axis. Although any one of these three bodies may be rotatable on the respective axes with which they are concentric, one of the three is held against rotation to provide a reaction torque whereas the other two bodies are rotatable and coupled either directly or by gearing to the respective input and output shafting of the transmission.
It is to be noted that the terms "alpha body," "beta body" and "omega body" are completely arbitrary and as such, do not restrict the components designated thereby either to the class of transmission represented by the disclosure of the aforementioned application or to specific structure to be described hereinafter. The terms will, however, lend consistency of definition in the description to follow and facilitate an understanding of various speed relationships to be expressed by algebraic equations.
The infinitely variable speed ratio capability of such transmissions is achieved by providing one of the beta and omega bodies with a pair of rolling or traction surfaces which are surfaces of revolution about the concentric body axis and which are of variable radii along that axis in symmetry with the point of first and second axes intersection. Physically, such rolling surfaces will thus provide the one body with a biconical-like configuration. The other of the beta and omega bodies is provided with a pair of rolling or traction surfaces which are also surfaces of revolution about the concentric body axis but which are of relatively constant radius. The pairs of rolling surfaces on the beta and omega bodies are retained in frictional engagement with each other at two contact points or zones capable of positional adjustment to vary the ratio of the beta body surface radius (R.sub.b) to the omega body surface radius (R.sub.w). Thus, if the alpha body is rotatable at a velocity (.alpha.) about the first axis, the rotational speed of the beta body about the second axis in a fixed frame of reference is (.beta.) and the rotational speed of the omega body on the first axis is (.omega.), then the respective speeds of the three bodies are related by the following equation: EQU .omega.-.alpha.+(.alpha.-.beta.)R.sub.b /R.sub.w =0 (1)
Because one of either the beta or the alpha body extends within the other of such bodies, the radius ratio R.sub.b /R.sub.w may represent a value of either less than 1 (where R.sub.b is always less than R.sub.w) or more than 1 (where R.sub.b is always greater than R.sub.w). The function .rho. will be used hereinafter to designate either R.sub.b /R.sub.w or the reciprocal R.sub.w /R.sub.b, whichever is greater than 1, it being understood that .rho. or its reciprocal 1/.rho. are used appropriately.
Heretofore, a generally preferred mode of operating such transmissions has been to apply an input torque to the alpha body to carry the beta body in nutation and hold the omega body against rotation (.omega.=0). The beta body is linked with an output shaft rotatable on the first axis by gearing having a ratio factor (k) which theoretically may be of any value and also may be made either positive or negative depending on the particular gearing arrangement used. In light of the foregoing, where .theta. is unit output speed and taking into account the gearing ratio (k), the output/input speed ratio of the unit is determined by an equation: EQU .theta./.alpha.=1-k.rho.. (2)
A principal advantage of operating in the mode represented by equation (2) is that the physical parameters of such I.V. transmissions readily accommodate a range of values for the function (k.rho.) which permit a continuously variable output/input speed ratio range of from zero to 1 (1.0&gt;k.rho.&gt;0.5). Also, this range may be shifted to include an output reversal through zero merely by selecting a gear ratio (k) so that the function (k.rho.) brackets a numerical value of 1 (e.g. 1.2&gt;k.rho.&gt;0.7).
In addition to the aforementioned copending application, reference is also made to commonly assigned U.S. Pat. No. Re. 29,328, reissued Aug. 2, 1977 in the name of Yves Jean Kemper; No. 4,112,779 and No. 4,112,780, the latter both having issued on Sept. 12, 1978, in the name of Yves Jean Kemper and Lucien Bigot. These issued patents disclose additional variations of the infinitely variable transmission type referred to above. As will be seen from these several prior patents, the particular configuration of any one of the alpha, beta and omega bodies as defined herein may vary in the respectively disclosed embodiments. It is also demonstrated by these prior developments as well as by the general equation of relative speeds given above as equation (1), that in a given embodiment, any one of the three working bodies may serve any one of the respective driving, driven or reaction torque functions. In no single embodiment, however, are these functions physically interchangeable without modification of structure.
The state-of-the-art relating to I.V. transmissions and systems incorporating same is further developed to a point where the speed ratio range of a unit may be enlarged by external epicyclic gearing in which the I.V. unit input and output are used as two inputs to the external epicyclic gearing in a way to drive a single system output shaft from the epicyclic gearing. Such systems, moreover, have accounted for synchronous operation in which the system may be shifted between one range of infinitely variable speed ratios with adjustment of the I.V. unit in one direction between the extreme limits of its radius ratio, and a second contiguous range of system speed ratios in which the I.V. unit is adjusted in the opposite direction between its limits of speed ratio variation. In this respect, see U.S. Pat. No. 3,406,597, issued Oct. 22, 1968, to F. G. De Brie Perry et al. While the use of such external epicyclic gearing to enlarge the speed ratio range available in an I.V. transmission unit solves the problem of expanding the range of speed ratios available in an I.V. transmission, epicyclic gear operation is objectionable from the standpoint of introducing efficiency losses in the system.